FIELD OF THE INVENTION
-
The present invention relates to disposable absorbent articles.
Disposable absorbent articles are designed to be worn externally of the
body by a user and to receive fluids discharged from the body, such as
disposable absorbent pantiliners, sanitary napkins, catamenials, and
incontinence inserts. Particularly the present invention relates to such
articles that exhibit an increased comfort for the user by showing a dilatant
behaviour, due to the use of a particulate material in such articles.
BACKGROUND OF THE INVENTION
-
In their basic form, disposable absorbent articles comprise an
absorbent core interposed between a pervious body-contacting element
(alternatively referred to as a topsheet or an overwrap) and an impervious
protective barrier (alternatively referred to as a backsheet). The absorbent
core is, of course, intended to receive and contain the fluids discharged
from the body. The body-contacting element is intended to provide
comfortable and dry-feeling contact with body surfaces while allowing free
passage of fluids therethrough into the absorbent element. The protective
barrier is intended to prevent the fluids which are expelled or which escape
from the absorbent element from soiling the user's garments.
-
Improved comfort for the user has been since long recognized as a
need for this category of products. Thin disposable absorbent articles,
typically featuring a thickness of less than 5 mm, are for example
appreciated since they are more comfortable and discreet. Improvements in
comfort in disposable absorbent articles, particularly in preferred thin
articles, have been usually achieved at the expense of the level of
protection of said articles. A softer article, that may be preferred in terms of
comfort, can in fact lead to twisting or bunching in use under the forces
exerted on it by the user's body and, possibly, by the undergarment, during
the movements normally experienced in the wearing time. This tendency is
even more pronounced in the wet state of the article, when structures of
disposable absorbent articles usually loose part of their original strength
and stability and are less capable of withstanding the stresses occurring in
use. The twisting and bunching is referred to as "roping" since a cylindrical
profile can be imparted to the absorbent article. The roping effect is
detrimental because the absorbent article is less capable of absorbing body
fluid that contact its upper surface. For example, the fluid discharged from
the vagina has in fact a tendency to run off the roped napkin before it can be
absorbed and, therefore, the fluid leaks onto the undergarment. This run-off
becomes significant during periods of heavy flow. Moreover, the roping
causes a reduction in the useful area of the absorbent article. Besides
being uncomfortable to the user, a twisted absorbent article has a smaller
strike zone to catch body fluids and thus is less effective in intercepting
them. This also results in more frequent leakage.
-
Providing a disposable absorbent article with a stiffer and/or more
resilient structure may solve on one hand the roping problem, since the
article is then more capable of resisting to the deformation induced by the
user's movements and/or of recovering its original optimal configuration
after deformation. This was suggested for example in US 4,217,901,
where the use of superabsorbent particles for providing increased crush
resistance was disclosed. This poses on the other hand a comfort issue
since the higher stiffness and/or resiliency make in any case the article
resist with an approximately constant force to the wearer's movements,
which in order to prevent bunching and twisting is typically sufficiently high
to cause discomfort.
-
It has now been found that the use of suitable particulate materials in
a disposable absorbent article is beneficial as far as comfort is concerned
since it can provide the article with a so called dilatant behaviour, or force
dependant resistance.
-
Particularly preferred particulate materials suitable to provide
dilatancy are some of the materials that are commonly used in disposable
absorbent articles as odour control agents.
-
Odour control has been another aspect of absorbent articles that has
been under investigation for many years. Many body fluids have an
unpleasant odour, or develop such odours when in contact with air and/or
bacteria for prolonged periods. The literature shows many references
relating to odour control in products such as diapers and catamenials. A
known solution to this problem is to incorporate an odour control agent in
the disposable absorbent article.
-
In a preferred mode, the odour-control agent is a water-insoluble
particulate odour-absorbing material such as chlorophyll particles, activated
carbon granules, charcoal, ion exchange resin (Japanese 87019865),
activated alumina, and absorbent zeolite materials, including the well
known "molecular sieve" zeolites of the type A and X and the zeolite
materials marketed under the trade name ABSCENTS by the Union
Carbide Corporation and UOP, and which are typically available as a white
powder in the 3-5 micron particle size range.
-
It has now been discovered that the incorporation in a disposable
absorbent article of certain preferred odour control agents in particulate
form not only provides an advantage in controlling the unpleasant odours
related to the body fluids absorbed, but also provides an unexpected benefit
in respect to comfort by giving the article a dilatant behaviour, both in the dry
and in the wet state, i.e., before and after absorption of body fluids during
the use.
-
Dilatancy is a rheological behaviour of a type of non-Newtonian
fluids, accordingly called dilatant fluids, in which the viscosity increases with
increasing shear rate. In other words, a dilatant fluid, or, more generically, a
dilatant system, opposes an increasing resistance to increasing shear
stresses. A well known example of a dilatant material is beach sand, both
dry and wet. When considering a dilatant behaviour in a disposable
absorbent article, it is meant that the article dynamically changes its
physical characteristics by increasing its resistance to deformation and/or its
resiliency under increasing stresses during wearing; the article therefore
shows a resistance to deformation that overall increases with the amount of
deformation. Dilatancy can in fact provide a disposable absorbent article
with the capability of better resisting to stresses applied with various speeds
during the use, or, alternatively, to prolonged stresses having a relatively
high intensity, to prevent bunching and twisting.
-
A disposable absorbent article provided with a dilatant behaviour has
therefore a low resistance to deformation at low levels of stress usually
involving a lower shear rate, while it increases its deformation resistance
when stresses induced by movements during the wearing time become
greater and cause higher shear rates in the article. This results in a better fit
during the use and in an increased resistance to bunching and twisting,
typically caused by higher levels of stress experienced by the article when
worn. The article is moreover more comfortable for the user, since it is
capable of following the wearer's movements adapting its deformation
resistance to the varying stresses to which it is subjected during the use.
-
The preferred particulate material incorporated in the disposable
absorbent articles of the present invention constitute a dilatant system both
in the dry and in the wet state, and this is particularly advantageous since
the particulate material can provide the article with dilatant behaviour also
in the wet state, i.e. after absorption of body fluid has taken place, when
usually the absorbent articles have a lower capacity to withstand twisting
and bunching.
SUMMARY OF THE INVENTION
-
The present invention relates to the use of a particulate material in a
disposable absorbent article for providing the article with dilatant behaviour,
in order to provide the article with a better resistance to bunching and
twisting in use.
BRIEF DESCRIPTION OF THE DRAWINGS
-
While the specification concludes with claims particularly pointing out
and distinctly claiming the present invention, it is believed that the present
invention will be better understood from the following description in
conjunction with the following drawings:
- FIG. 1 is a plan view of a sanitary napkin according to the present
invention, seen from the side thereof that faces the wearer in use;
- FIG. 2 is a graph showing how the force necessary for a deformation
of the sanitary napkin varies with the amount of deformation in the dry state;
- FIG. 3 is a similar graph showing the same dependency in the wet
state.
-
DETAILED DESCRIPTION OF THE INVENTION
-
This invention relates to disposable absorbent articles for application
to the user's body, which exhibit absorbency for bodily fluids, the protection
of the user's garments from soiling, and improved physical comfort to the
user.
-
As used herein, the term "absorbent article" refers to devices which
absorb and contain body exudates, and, more specifically, refers to devices
which are placed against or in proximity to the body of the wearer to absorb
and contain the various exudates discharged from the body. The term
"disposable" is used herein to describe absorbent articles which are not
intended to be laundered or otherwise restored or reused as an absorbent
article (i.e., they are intended to be discarded after a single use and,
preferably, to be recycled, composted or otherwise disposed of in an
environmentally compatible manner). A preferred embodiment of an
absorbent article of the present invention is the sanitary napkin 20 shown in
Fig. 1, where portions of the structure have been cut-away to more clearly
show the construction of the sanitary napkin 20 and with the portion of the
sanitary napkin 20 which faces or contacts the wearer oriented towards the
viewer. As used herein, the terms "pantiliner", and "sanitary napkin" refer to
absorbent articles generally worn by females adjacent to the pudendal
region that are intended to absorb and contain the various exudates which
are discharged from the body (e.g., vaginal discharges, blood, menses, and
urine). The present invention, however, is not limited to the particular types
or configurations of absorbent articles shown in the drawing. It should be
understood that the present invention is also applicable to other
anatomically shaped disposable absorbent articles such as incontinent
pads, and the like.
-
The term "use", as used herein, refers to the period of time that starts
when the absorbent article is actually put in contact with the anatomy of the
user.
-
The terms "joined", "affixed" or "secured", as used herein,
encompasses configurations whereby a first member is directly connected
to a second member and configurations whereby a first member is indirectly
connected to a second member by connecting the first member to
intermediate members which in turn are connected to the second member.
-
As used herein, the term "pudendal" refers to the externally visible
female genitalia and is limited to the labia majora, the labia minora, the
clitoris, and the vestibule.
-
As shown in Fig. 1, the sanitary napkin 20 comprises an absorbent
means represented by main body portion 22. The main body portion 22 has
longitudinal edges 24 and lateral edges 26. The term "longitudinal", as
used herein, refers to a line, axis or direction in the plane of the sanitary
napkin 20 that is generally aligned with (e.g., approximately parallel to) a
vertical plane which bisects a standing wearer into left and right body
halves when the sanitary napkin 20 is worn. The term "lateral" as used
herein, refers to a line, axis or direction which lies within the plane of the
sanitary napkin 20 that is generally perpendicular to the longitudinal
direction.
-
The main body portion 22 comprises a topsheet 30, a backsheet 50,
and an absorbent core 60.
-
The topsheet 30 is liquid permeable and when the sanitary napkin 20
is in use, the topsheet 30 is compliant, soft feeling, and non-irritating to the
user's skin. Further, the topsheet 30 is liquid pervious, permitting liquid (e.g.
menses and/or urine) to readily penetrate through its thickness. A suitable
topsheet 30 may be manufactured from a wide range of materials such as
woven and nonwoven materials; polymeric materials such as apertured
formed thermoplastic films, apertured plastic films, and hydroformed
thermoplastic films; porous foams; reticulated foams; reticulated
thermoplastic films; and thermoplastic scrims. Suitable woven and
nonwoven materials can be comprised of natural fibres (e.g., wood or cotton
fibers), synthetic fibres (e.g., polymeric fibres such as polyester,
polypropylene, or polyethylene fibres); or from a combination of natural and
synthetic fibres.
-
A preferred topsheet comprises an apertured formed film. Apertured
formed films are preferred for the topsheet because they are pervious to
body fluids and yet non-absorbent and have a reduced tendency to allow
liquids to pass back through and rewet the wearers skin. Thus, the surface
of the formed film which is in contact with the body remains dry, thereby
reducing body soiling and creating a more comfortable feel for the wearer.
-
Suitable formed films are described in U.S. Pat. No. 3,929,135,
issued to Thompson on December 30, 1975; U.S. Pat. No. 4,324,246,
issued to Mullane, et al. on April 13, 1982; U.S. Pat. No. 4,342,314, issued
to Radel, et al. on August 3, 1982; U.S. Pat. No. 4,463,045, issued to Ahr, et
al. on July 31, 1984; and U.S. Pat. No. 5,006,394, issued to Baird on April 9,
1991. A preferred topsheet for the absorbent article of the present invention
is a formed film described in one or more of the above patents and
marketed on sanitary napkins by The Procter & Gamble Company of
Cincinnati, Ohio as "DRI-WEAVE".
-
Topsheets having not a homogeneous distribution of liquid passage
ways but only a portion of the topsheet comprising liquid passage ways are
also contemplated by the present invention. Typically such topsheets would
have the liquid passage ways oriented such that they result in a centrally
permeable and peripherally impermeable topsheet for liquids.
-
In a preferred embodiment of the present invention, the body or
exposed surface of the formed film topsheet is hydrophilic so as to help
liquid transfer through the topsheet faster than if the body surface were not
hydrophilic so as to diminish the likelihood that menstrual fluid will flow off
the topsheet rather than flowing into and being absorbed by the absorbent
core. In a preferred embodiment, surfactant is incorporated into the
polymeric materials of the formed film topsheet such as is described in PCT
publication WO 93/09741. Alternatively, the body surface of the topsheet
can be made hydrophilic by treating it with a surfactant such as is described
in U.S. 4,950,254.
-
Another alternative are so called hybrid topsheets which incorporate
fibrous and film like structures particularly useful embodiments of such
hybrid topsheets are disclosed in PCT publications WO 93/09744, WO
93/11725 or WO 93/11726.
-
When referring to the topsheet a multi layer structure or a mono layer
structure is contemplated. The hybrid topsheet mentioned above is such a
multi layer design but other multi layer topsheets such as primary and
secondary topsheet designs are also considered.
-
The absorbent core 60 is positioned between the topsheet 30 and
the backsheet 50. The absorbent core 60 provides the means for absorbing
body fluids. The absorbent core 60 need not have an absorbent capacity
much greater than the total amount of body fluid anticipated to be absorbed.
The total absorbent capacity of the absorbent core should usually be
compatible with the design leading and the intended use of the absorbent
article. Further, the size and absorbent capacity of the absorbent core may
be varied to accommodate different uses. A sanitary napkin as that
illustrated in FIG. 1, for example, will have generally larger dimensions, and
will comprise an absorbent core 60 with a higher absorbent capacity, as
compared to a pantiliner. The absorbent core 60 is generally compressible,
conformable, and non-irritating to the user's skin. It can comprise any
material used in the art for such purpose. Examples include comminuted
wood pulp which is generally referred to as airfelt, creped cellulose
wadding, absorbent foams, absorbent sponges, synthetic staple fibres,
polymeric fibres, hydrogel-forming polymer absorbent gelling materials,
peat moss, or any equivalent material or combinations of materials. The
absorbent core may also have a layer of absorbent gelling material, such as
in the form of particles, disposed between two air-laid tissue layers (or
"upper" and "lower" tissue layers). The first and second tissue layers
provide containment of the absorbent gelling material, improved lateral
wicking of the absorbed exudates throughout the absorbent core, and a
degree of absorbency. Exemplary absorbent structures for use as the
absorbent core of the present invention are described in U.S. Patent
4,950,264 entitled "Thin, Flexible Sanitary Napkin" issued to Osborn on
August 21, 1990; U.S. Patent 4,610,678 entitled "High-Density Absorbent
Structures" issued to Weisman et al. on September 9, 1986; U.S. Patent
4,834,735 entitled "High Density Absorbent Members Having Lower Density
and Lower Basis Weight Acquisition Zones", issued to Alemany et al. on
May 30, 1989; and European Patent Application No. 0198 683, the Procter
& Gamble Company, published October 22, 1986 in the name of Duenk, et
al.
-
In a preferred embodiment of the present invention illustrated in FIG.
1 the absorbent core 60 is constituted by a layered structure in accordance
with the disclosure of WO 94/01069 or WO 95/17868, that describe a thin,
layered absorbent structure comprising first and second layers 61, 62 of
fibrous material, e.g. air laid material, and an intermediate layer 63
comprising particles of absorbent gelling material 64 and particles of a
thermoplastic, polymeric material 65; the first and second fibrous layers 61,
62 extend beyond the intermediate layer 63 laterally to form longitudinal
edge portions 66. The two fibrous layers 61, 62 are bound together with the
intermediate layer 63 between them by the melting of the particles of
thermoplastic, polymeric, organic material 65 and by means of a continuous
line 67 of adhesive extending longitudinally on each edge portion 66.
-
WO 95/17868 describes a layered structure substantially as
described in WO 94/01069 with the exception that WO 95/17868 comprises
a much higher quantity of absorbent gelling material in the intermediate
layer which is between the fibrous layers, namely in an amount exceeding
120 g/m2.
-
Absorbent gelling materials mentioned above are those materials
which, upon contact with fluids (i.e., liquids) such as water or body fluids,
imbibe such fluids and thereby form hydrogels. In this manner, fluids
discharged into the absorbent core 60 can be acquired and held by the
absorbent gelling materials, thereby providing the articles herein with
enhanced absorbent capacity and/or improved fluid retention performance.
Preferred absorbent gelling materials which are employed in the absorbent
core 60 will generally comprise particles of a substantially water-insoluble,
slightly cross-linked, preferably neutralized, hydrogel-forming polymer
material. The term "particles", as used herein, can refer to particles in any
form, such as in the form of pellets, flakes, or fibres. The characteristics of
the absorbent core 60 (including, but not limited to preferred types of
polymer materials used herein, and types of methods which can be used for
preparing these polymer particles) are described in greater detail in U.S.
Patent 5,009,653 issued to Osborn.
-
The sanitary napkin 20 of the present invention further comprises,
e.g. in the absorbent core 60, mixed with the particles of absorbent gelling
material 64 and of thermoplastic, polymeric material 65, an odour-control
material for controlling unpleasant odours associated with absorbed body
fluids.
-
Any known odour-control agent or any combination thereof that can
be suitably included in a disposable absorbent article, including other
materials such as binders and/or substrates, can be comprised in the
sanitary napkin 20 of the present invention as the odour-control material.
-
The odour-control material can be incorporated into the sanitary
napkin 20 by methods known in the art, for example layered in the
intermediate layer 63 of the absorbent core 60.
-
The absorbent articles according to the present invention comprise a
backsheet 50 that is impervious to liquids (e.g. menses, vaginal discharges,
and/or urine) and is preferably manufactured from a thin plastic film,
although other flexible liquid impervious materials can also be used. In use,
the backsheet 50 is interposed between the absorbent core 60 and the
user's undergarments. The function of the backsheet 50 is to prevent
exudates which may be expelled from or which inadvertently bypass the
absorbent core 60 from contacting and soiling the user's undergarments.
The backsheet 50 can thus comprise a woven or nonwoven material,
polymeric films such as thermoplastic films of polyethylene or
polypropylene, or composite materials such as a film-coated nonwoven
material. Preferably, the backsheet is a polyethylene film having a
thickness of from about 0.012 mm to about 0.015 mm. Exemplary
polyethylene films are manufactured by Clopay Corporation of Cincinnati,
Ohio, under the designation P18-0401 and by Ethyl Corporation, Visqueen
Division, of Terre Haute, Indiana, under the designation XP-39385. The
backsheet 50 is preferably embossed and/or matte finished to provide a
more clothlike appearance. Further, the backsheet 50 may permit vapours
to escape from the absorbent core 60 (i.e., it can be breathable) while still
preventing exudates from passing through the backsheet 50.
-
The backsheet 50 typically extends across the whole of the main
body portion 22 of the sanitary napkin 20.
-
The topsheet, backsheet and absorbent core elements are joined
together to provide the sanitary napkin 20 of the present invention. At least
two, preferably all of the elements of the sanitary napkin 20 are joined.
-
Each of said elements comprising at least one layer has a body
facing surface and a garment facing surface. Typically, adjacent garment
facing surfaces form a common interface with the body facing surface of an
adjacent element or layer. The elements or layers are joined together
across this common interface. In this manner the topsheet 30 is joined to
the absorbent core 60, and the core 60 is joined to the backsheet 50.
Furthermore, each of said topsheet 30, backsheet 50 and core 60 elements
may comprise more than one layer and these layers may also be similarly
joined. In addition the topsheet 30 is directly or indirectly joined to the
backsheet 50 at the periphery of the sanitary napkin 20.
-
The elements and layers thereof may be joined by any means known
in the art for affixing two adjacent layers of material, such that the layers are
directly attached to one another or directly attached to one another via the
joining means. Suitable joining means include adhesive, fusion bonding,
ultra sonic bonding, stitching, heat (e.g. crimping), embossing, and/or
pressure bonds, or dynamic mechanical bonds. According to an
embodiment of the present invention the preferred means of joining is
adhesive. Suitable adhesives include non pressure sensitive and cold
adhesives. The adhesive may be applied by any means known in the art
such as spiral application, slot coating, spraying, spiral spraying, curtain
coating, control coating and printing.
-
In a preferred embodiment of the present invention wherein the
absorbent article finds utility as a sanitary napkin 20, the absorbent article is
also provided with a panty fastening means which provides means to attach
the article to an undergarment. For example the panty fastening means
may comprise a mechanical fastener such as hook and loop fasteners such
as marketed under the tradename VELCRO, snaps or holders.
Alternatively, the article is fastened to the undergarment by means of panty
fastening adhesive on the backsheet 50. The panty fastening adhesive
provides a means for securing the article to the panty and preferably a
means for securing the article when soiled, to the fold and wrap package for
convenient disposal. Typically, at least a portion of the garment facing
surface of the backsheet 50 is coated with adhesive to form the panty
fastening adhesive. Any adhesive or glue used in the art for such purposes
can be used for the panty fastening adhesive herein. Pressure sensitive
adhesives are most preferred. Suitable adhesives include Century A-305-IV
manufactured by the Century Adhesives Corporation of Columbus, Ohio,
and Instant LOK 34-2823 manufactured by the National Starch and
Chemical Company of Bridgewater, New Jersey, 3 Sigma 3153
manufactured by 3 Sigma and Fuller H-2238ZP manufactured by the H.B.
Fuller Co.
-
The panty fastening adhesive is applied to the backsheet 50 by any
means and with any distribution known in the art.
-
The panty fastening adhesive is typically covered with a removable
release paper or film in order to prevent the adhesive from drying out or
adhering to another surface other than the panty prior to use. Any
commercially available release paper or film may be used. Suitable
examples include BL 30MG-A SILOX EI/O and BL 30 MG-A SILOX 4 P/O
available from Akrosil Corporation.
-
According to the present invention, the sanitary napkin 20 is provided
with a dilatant behaviour by means of the use of a suitable particulate
material incorporated therein. Dilatancy gives the disposable absorbent
article of the present invention, e.g. the sanitary napkin 20, the property of
increasing its stiffness, i.e. its capability to withstand deformation, when
subjected to increasing stresses, involving higher shear rates in the
particulate material, caused by the wearers movements during the wearing
time. This results in a product that deforms easily and smoothly under
stresses involving lower shear rates which usually cause small
deformations, therefore being comfortable to the wearer, but is less subject
to deformation under higher stresses, that are more likely to cause
permanent deformations in a traditional product, e.g. bunching or twisting as
a result of compression forces exerted in transverse direction on the
sanitary napkin by the wearer's thighs. The article provided with dilatancy is
in other words more capable of resisting to stresses applied with various,
e.g. increasing, speeds during the use, and also to prolonged stresses
having higher intensities.
-
Bunching and twisting in use usually lead to a sanitary napkin 20
crushed transversely inwardly with its longitudinal edges 24 curled around
its longitudinal axis, so that the napkin eventually takes on the appearance
of a twisted rope, particularly in its central portion. The phenomenon is in
fact known as roping, and causes a reduction of the useful surface of the
absorbent article, and therefore of both its absorption capacity and of its
capability of properly acquiring the body fluids as they are discharged. The
article is also uncomfortable to the wearer since it becomes thicker and is
therefore less soft and conformable.
-
Absorbent articles of thin type, typically having a thickness of less
than 5 mm, have a particular tendency to roping when worn, as a result of
the squeezing of the article between the thighs of the wearer, which can
cause a permanent deformation.
-
Suitable materials that can be incorporated in a disposable
absorbent article according to the present invention in order to provide
dilatancy could be in principle those materials, usually in particulate or
suspension form, e.g. water suspension, that are known as forming dilatant
systems. Suitable materials are typically non swellable particulate
materials.
-
According to the present invention, it has been found that some of the
preferred odour control materials that are incorporated in particle form in
disposable absorbent articles are not only active in controlling the
unpleasant odours associated with the absorbed body fluids, but also
involve a further benefit in terms of comfort and effectiveness of the article
by providing the disposable absorbent article with the dilatant behaviour,
both in dry and in wet state, i.e., before and after absorption of body fluids
during the use.
-
Particularly preferred are odour control substances such as silica,
zeolites, including the molecular sieve zeolites of the type A, starch,
aluminium oxide (alumina), activated carbon, and mixtures or agglomerates
thereof. Quartz powder and polyethylene powder can also be used, even
though they alone cannot provide the odour control benefit. Any
combination with other known odour control substances, not related to
dilatancy, is also possible.
-
The particulate material for providing dilatancy can be incorporated
in different amounts and different particle sizes, and according to that
different levels of dilatancy can be achieved, as can determined by the man
skilled in the art. The particles can be of any desired suitable shape.
-
Preferably, the average dimensions of the particulate material used
in a disposable absorbent article according to the present invention, given
as a weighted average of the smallest dimensions of the individual
particles, can be between 50 microns and 1500 microns, preferably
between 100 microns and 800 microns.
-
Preferred odour control materials in particulate form that are also
capable of providing an absorbent article such as the sanitary napkin 20 of
the present invention with a dilatant behaviour can be among those
described in European Patent Applications EP 96109173.3,
EP 96109174.1, EP 96109175.8, EP 96109176.6, EP 96109177.4. Most
preferred odour control materials in particulate form also providing dilatancy
comprise zeolite A and silica gel.
-
In a preferred embodiment of the present invention, a particulate
material 68 comprising zeolite A and silica gel intended to provide odour
control and dilatancy is comprised in the intermediate layer 63 of the
absorbent core 60, mixed with particles of absorbent gelling material 64.
The amounts of the absorbent gelling material particles 64 and of the
particulate material for providing odour control and dilatancy can
respectively range from about 20 g/m2, up to about 600 g/m2, and from
about 40 g/m2 and about 200 g/m2.
-
The dilatant behaviour provided by the particulate material 68 in the
sanitary napkin 20 of the present invention can be evaluated, both in the dry
and in the wet state, by a compression test performed on the sanitary napkin
20. The test actually measures the force necessary to deform, i.e., to bend,
in longitudinal direction a sanitary napkin 20 featuring a dilatant behaviour,
as a function of the amount of the deformation induced at constant speed;
the test therefore measures the resistance of the sanitary napkin to forces
directed transversely, as those exerted in use by the inner part of the
wearer's thighs. The results have been compared to those obtained with a
reference sample comprising no particulate material for providing dilatancy.
Samples
-
Both the reference sample and the sample according to the present
invention used in the compression test were sanitary napkins of the type
Always Ultra currently available on the market, having the absorbent core
replaced by a layered structure 70 mm wide made according to the
disclosure of WO 94/01069. The layered structure incorporated in the
reference sample comprises a first and second fibrous layer, each
constituted by an airlaid nonwoven web having a basis weight of 60 g/m2,
and an intermediate layer comprising particles of absorbent gelling material
in an amount of 63.80 g/m2. The layered core structure of the reference
sample is currently sold by Korma, Italy, under the code XA07001001. The
layered structure comprised in the sanitary napkin according to the present
invention differs form the layered structure of the reference sample in that it
further comprises in the intermediate layer particles of zeolite A in an
amount of 61.50 g/m2, and particles of silica gel in an amount of
86.37 g/m2 in order to provide dilatancy, homogeneously mixed with the
particles of absorbent gelling material. The release paper is removed from
each sample and the panty fastening adhesive is neutralized with talc.
Each side flap is cut with scissors along a line parallel to the respective
longitudinal edge of the absorbent core.
Compression test, dry
-
The apparatus used for the test is an INSTRON 6021 Dynamometer
(Tensile Tester), with the load cell calibration set at 10 N; the compression
speed is set at 100 mm/min and the Tensile Tester is set to run a
Compression test; the clamp distance is set at 65 mm. Each sample is
positioned symmetrically between the fixed and the moving clamp, with
each clamp holding a portion of the absorbent core 2.5 mm wide along the
respective longitudinal edge, and with the topsheet facing the operator. The
initial force exerted on the sample is less than 0.100 N. The sample is
slightly biased in order to have it bend in longitudinal direction during
compression with the convexity on the topsheet side.
-
The test is run and the force in N exerted by the sample on the
moving clamp is recorded on a graph, shown in FIG. 2, as a function of the
sample deformation, i.e., of the distance between the clamps.
Compression test, wet
-
After the compression test in dry conditions the same sample is
removed from the clamps of the tester and put onto a flat plate; 12 ml of PIF
fluid are released onto the centre of the product at a flow rate of 8 ml/min,
and the sample is left on the plate for 20 minutes. Then the sample is
compressed for 15 sec with a weight exerting a pressure of 70 g/cm2 on a
surface of 4.5x10 cm centered on the sample itself, and the compression
test is repeated with the same procedure as described for the dry state. The
force is recorded on the similar graph of FIG. 3 as a function of the
deformation.
-
In both graphs of FIGS. 2 and 3 the reference sample has been
identified as "Reference", while the sample according to the present
invention has been identified as "Dilatant".
Preparation of Test Solution Paper Industry Fluid (PIF)
-
The test solution PIF is a widely used test liquid in the Paper industry
due to its simple composition, ability to prepare and maintain high
standards of solution quality and its similarity to human menses with respect
to viscosity and ionic surface tension.
-
The solution PIF is prepared by dissolving the following reagent
components, at the indicated quantities, into 1 litre of distilled water. Care
should be taken in dissolving the solid components and particularly the
Carboxylmethylcellulose. Typically the solid components should be added
over a period of one hour slowly and with constant stirring of the solution
(via a magnetic stirring device).
-
Supplier Sigma Chemicals, USA
Chemical Component | Usage / 1L |
1) | Carboxymethylcellulose, Sodium salt low viscosity: Order No. = C 5678, | 15 grams |
2) | Sodium bi-Carbonate, Crystalline: Order No. = S 8875 | 4 grams |
3) | Sodium Chloride (AR): Order No. = S 9625 | 10 grams |
4) | Glycerol (>99% pure): Order No. = G 5516 | 80 grams |
-
The results of the Compression test in dry and wet conditions are
illustrated in the two graphs of FIGS. 2 and 3, respectively.
-
In both graphs the force opposed by the dilatant sanitary napkin at
very low compressions, where the dilatant behaviour is much less evident,
is higher as compared to the force opposed by the reference sample,
because the dilatant sample comprises a higher basis weight of particulate
material as compared to the reference sample, and therefore possibly the
bonding action performed by the melting of the thermoplastic, polymeric,
organic material particles is proportionally higher, since the amount of the
melting particles is a given percentage of the total amount of the mixture.
-
Anyway, FIGS. 2 and 3 show how the force opposed to the
compression in transverse direction (deformation along a longitudinal
direction) increases with the increasing deformation much more in the
sanitary napkin provided with the dilatant behaviour as compared to the
reference sample, both in the dry and in the wet state. For example, the
difference between the forces exerted by the dilatant sanitary napkin and by
the reference sample in correspondence of a distance between the clamps
of 20 mm, is about twice as much the same difference at a deformation of
10 mm. Of course the absolute values of the force are on average lower in
the wet state, where the strength of the structure against deformation is
overall lower.
-
The test demonstrates that the dilatant behaviour provided by the
preferred odour control particulate material gives the product a better
capacity to withstand permanent deformations induced by increasing forces
exerted by the body as it moves during the wearing time, not only in the dry
state of the article, but also in the wet state, i.e., after absorption of fluid,
when usually the structures of disposable absorbent articles become
weaker and less resistant to twisting and bunching (roping).
-
The particulate material capable of providing the disposable
absorbent article of the present invention with the dilatant behaviour can be
alternatively comprised in any other location within the absorbent article,
other than in the absorbent core, but preferably in a position that allows the
particulate material to come in contact with body fluid during the use.
-
Without being bound to any theory, it is in fact believed that when the
liquid contacts the particulate material this creates a dilatant suspension
and a more effective dilatant system is provided.
-
Although the present invention has been so far described in the
context of substantially planar disposable absorbent articles, it can be
alternatively applied to tridimensionally shaped disposable absorbent
articles, both those having a pre formed shape prior to use, and those that
are capable of shaping and forming in use.
-
In an alternate embodiment of the present invention, the disposable
absorbent article may have two flaps (not shown), each of which is adjacent
to and extends laterally from the respective side edge of the absorbent core.
The flaps are configured to drape over the edges of the wearer's panties in
the crotch region so that the flaps are disposed between the edges of the
wearer's panties and the wearer's thighs. The flaps help serve to prevent
soiling of the wearer's body and panties by menstrual fluid, preferably by
forming a double wall barrier along the edges of the panty. The flaps may
be also provided with attachment means on their garment facing surface so
that the flaps can be folded back under the panty and attached to the
garment facing side of the panty.
-
The flaps may be constructed of various materials including materials
used for the topsheet 30, backsheet 50, combinations thereof, and may be a
laminate having tissue in the centre. Further, the flaps may be a separate
element attached to the main body of the tridimensional absorbent article or
can comprise extensions of the topsheet 30 and/or backsheet 50. It is
recommended, however, that the flaps have a liquid impervious backsheet
to prevent body fluids which reach the flaps from soiling the edges of the
wearer's panties. Even though the area of the flaps can be considered as
portions of the article comprising at least the topsheet and the backsheet
extending beyond the absorbent core, it is generally meant that the flaps do
not constitutes lobes, in the sense intended according to the present
invention.
-
Preferred flaps that are suitable or adaptable to the tridimensional
absorbent article of the present invention are disclosed in U.S. Pat. No.
4,687,478 issued to Van Tilburg on Aug. 18, 1987; U.S. Pat. No. 4,589,876
issued to Van Tilburg on May 20, 1986; and U.S. Pat No. 4,608,047 issued
to Mattingly on Aug. 26, 1986.
-
Optionally, the absorbent article may comprise components that
naturally wrap the sides of a wearer's panties. Sanitary napkins having
components that naturally wrap the sides of a wearer's panties suitable for
use with the tridimensional absorbent article of the present invention are
disclosed in U.S. Patent No. 5,584,829 entitled "Absorbent Article having
Panty Covering Components that Naturally Wrap the Sides of Panties",
issued to Lavash, et al. on Dec. 17, 1996, and U.S. Patent No. 5,558,663
entitled "Absorbent Articles Having Undergarment Covering Components
with Zones of Extensibility", issued to Weinberger, et al. on Sep. 24, 1996.
-
Although the anatomically shaped disposable absorbent article of the
present invention has been described with reference to a sanitary napkin, it
can be used beneficially in the context of other disposable absorbent
articles such as sanitary napkins and incontinence articles. The disposable
absorbent article may thus also have all those features and parts which are
typical for products in the context of their intended use.